Input: i8042 - select ARCH_MIGHT_HAVE_PC_SERIO for SH_CAYMAN

Architectures which might use an i8042 for serial IO to keyboard,
mouse, etc should select ARCH_MIGHT_HAVE_PC_SERIO. Cayman board
is only sh board which needs this.

Signed-off-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>